I could not give less of a fuck about the school setting if I tried. Janna and Jackie are the only truly interesting characters from there and understandably they also have the most focus, and most importantly appearances actually outside the school.
I would like to see more Mewni, as it offers potential more than a fuckin' dumb high school, but we haven't seen enough of Mewni to know about its inhabitants at all, minus prominent secondaries like Moon, Ludo, etc. That could change in the next seasons and I'd enjoy that.
Unfortunately I'd say a flaw of this show is that Earth in this show is BORING, boring as all hell, and it seems a waste to focus on it more. Because, to the show's credit, the strong focus on Marco/Star antics keeps the focus away from the dull setting, not to mention the plot/lore episodes that are understandably much more interesting through not revolving around fuckin' Earth.
Even now I still really have no sense of what Earth "is" in this show. There's Marco's house, I know that pretty well, and the school, as boring as it is. But what else? It hardly feels like there are consistent settings--there's that taco place in S2 I guess, and they went to the park a few times. But where do Star and Marco like to hang out, what do they think about different places, etc.? The characters returning to the river (?) in Just Friends stood out through making use of an existing setting, for once. Maybe I'd care more if they actually focused on that, but they didn't and so I don't. Earth seems deliberately boring so Star contrasts with it.
We haven't seen much Mewni either, but the Tapestry Room and monster temples and castle are already more interesting than a taco place. Just the pink sky and three moons with the asteroids seem way more interesting, and those are just a constant background feature
Would I have liked if they'd fleshed out Earth more? Yeah maybe, but by now it's too late to care since they didn't exactly do an amazing job anyway.